1. Field of the Invention
The invention relates to a motor-driven prosthetic prehensor, more particularly to a motor-driven prosthetic prehensor that is provided with a self-locking mechanism to enable the user to grasp an object tightly.
2. Description of the Related Art
A conventional motor-driven prosthetic prehensor generally includes a motor, a thumb member, and a fingers assembly. When the conventional prosthetic prehensor is used to grasp an object, a motor is operated to move the thumb member and the fingers assembly toward each other and is instantly stopped once the thumb member and the fingers assembly come into contact with the object to be grasped so as to prevent breaking or damaging of the object. However, when a conventional prosthetic prehensor as such is used to grasp a relatively heavy object, the thumb member and the fingers assembly may displace undesirably due to lack of a braking force, thus resulting in dropping of the object held therebetween.
Therefore, the main object of the present invention is to provide a motor-driven prosthetic prehensor that is equipped with a self-locking mechanism to permit firm grasping of an object.
Accordingly, the motor-driven prosthetic prehensor of the present invention comprises a mounting frame that includes an upright annular member and an annular retaining member. The upright annular member has a periphery, front and rear mounting walls opposite to each other in an axial direction, and an inner annular bearing wall disposed in the front mounting wall and confining an axial hole extending along a first axis parallel to the axial direction to communicate the front mounting wall with the rear mounting wall. The retaining member has an inner annular friction wall, which is disposed to extend forwardly from the periphery of the upright annular member. The friction wall and the front mounting wall together define an accommodation space. A transmission shaft is rotatably mounted on the bearing wall of the upright annular member, and includes a front segment extending forwardly of the front mounting wall, and a rear segment extending rearwardly of the rear mounting wall. A coupling sleeve member is rotatably mounted on the front segment of the transmission shaft about the first axis, and has front and rear major walls opposite to each other in the axial direction, a toothed rim wall joining and peripheral to the front and rear major walls, and a plurality of driving blocks angularly displaced from one another and disposed on the rear major wall to extend rearwardly and axially into the accommodation space. A rotatable coupling member is mounted on and rotatable with the front segment of the transmission shaft, and is interposed between the rear major wall of the coupling sleeve member and the front mounting wall of the upright annular member. The coupling member includes a hub portion about the first axis and a plurality of driven spacer members that extend radially and outwardly from the hub portion, and that are angularly spaced apart from one another so as to cooperate with the friction wall of the retaining member to define a plurality of chambers for receiving the driving blocks of the coupling sleeve member, respectively. Each driving block is angularly spaced from a respective one of the driven spacer members by a guideway. A plurality of friction brake members are disposed respectively in the chambers, and are movable slidably along the guideways between an unobstructed position, where the friction brake members are pushed by the driving blocks on the rear major wall of the coupling sleeve member to move angularly and radially towards the first axis and to drive the driven spacer members and the transmission shaft to rotate in a clockwise or counterclockwise direction when the coupling sleeve member is rotated in the clockwise or counterclockwise direction such that the friction brake members steer clear of frictional contact with the friction wall of the retaining member, and a braked position, where the friction brake members are brought to engage and to be retained by the friction wall once the transmission shaft is hindered from rotating freely with the driving blocks. A plurality of biasing members are each disposed between a respective one of the friction brake members and a respective one of the driven spacer members to bias the respective friction brake member to move towards a respective driving block such that once the transmission shaft is hindered from rotating with the driving blocks, the biasing members will bias the respective friction brake member to move away from the respective driven spacer member and to move radially to engage the friction wall of the retaining member so as to arrest any further rotation of the coupling sleeve member in the clockwise or counterclockwise direction. A motor has an output shaft rotatably mounted on the mounting frame. A drive gear is mounted on the output shaft, and is disposed to mesh with the toothed rim wall of the coupling sleeve member so as to drive the coupling sleeve member to rotate. A thumb member is pivotally mounted on the mounting frame about a first pivoting axis. A fingers assembly is pivotally mounted on the mounting frame about a second pivoting axis, and is spaced apart from the thumb member in a direction transverse to the axial direction. A coupling mechanism is disposed to transmit driven rotation of the transmission shaft to drive the thumb member and the fingers assembly to turn about the first and second pivoting axes, respectively, and to move toward or away from each other so as to grasp or release an object.